The sound of an explosion on the surface of a lake is heard by a boat man 100 m away and by a diver 100 m below the point of explosion.

(i) Who would hear the sound first — boat man or diver?
(ii) Give a reason for your answer in part (i)
(iii) If sound takes time t to reach the boat man, how much time approximately does it take to reach the diver?

(i) The diver would hear the sound first.

(ii) The sound is heard by the diver first because sound travels faster in water than in air.

(iii) As we know, the speed of sound in water (1450 ms^-1 ) is more than the speed of sound in air (330 ms^-1) so if 't' is the time taken by sound to reach the boat man, then the time taken by sound to reach the diver is 0.25t as sound travels nearly four times faster in water.